Power management is becoming increasingly important as electronic devices place greater reliance on battery power. Portable computers, personal data assistants (PDAs), tablet computers, cellular phones, pagers, and wireless computer peripherals are only a few examples. While components of such devices are becoming increasingly power hungry, the demand for longer intervals between battery replacement or recharging has increased. Indeed, many devices are often turned on for ready usability but left idle for significant periods of time. Accordingly, there is an increasing need for systems and methods that reduce or slow battery depletion.
Wireless peripheral devices intended for use with a host computer are becoming more common. In particular, cursor control (pointing) devices such as a computer mouse can be made wireless by inclusion of a battery power source within the device and providing a wireless data link to a personal computer or other device via, e.g., an infrared or RF transmitter/receiver pair. Without effective power management, however, continuously operating a wireless peripheral can rapidly deplete the device's battery power, thereby requiring frequent battery replacement or recharging.
A common method of minimizing power consumption is to configure a device to “sleep” when it is not being used. In other words, a device may turn off many of its components during periods of non-use, and turn those components back on when the device is used. In a wireless computer mouse employing mechanical encoder wheels moved by a roller ball, sleep can occur by powering down the mouse's transmitter and receiver components, as well as other components not currently needed. The mouse can then periodically sample the encoder wheels for movement. When a change is detected in encoder wheel position between sampling intervals, the device “wakes up” and reactivates any powered-down components. This sampling occurs at a rate that is fast in comparison to human response time (on the order of 50 millisecond (msec) intervals); moving the mouse thus “wakes” the device without a perceptible delay. After experiencing a designated period of no motion, the mouse can then go back to sleep. The inactive intervals between sampling allow the average power use during “sleep” to be very small.
In another line of technological development, cursor control devices utilize optical surface tracking systems in lieu of conventional encoder wheel arrangements. Exemplary optical tracking systems, and associated signal processing techniques, include those disclosed in commonly owned U.S. Pat. No. 6,172,354 (Adan et al.) and copending application Ser. No. 09/692,120, filed Oct. 19, 2000, and Ser. No. 09/273,899, filed Mar. 22, 1999. Optical tracking can provide more reliable and accurate tracking by eliminating moving parts (e.g., a ball and associated encoder wheels) which are prone to malfunction from the pick-up of dirt, oils, etc. from the tracked support surface and/or a user's hand. On the other hand, optical tracking requires considerable power for driving the circuitry used to illuminate a trackable surface and to receive and process light (image information) reflected from the trackable surface.
Although optical mice and other cursor control devices are an improvement over devices relying upon mechanical encoder wheels, sampling mouse motion as a method of “waking” a sleeping optical mouse is problematic. To determine motion, the imager must be powered and compare at least two successive images to determine motion. This requires a motion detector's illuminating LED to be turned on for a significant amount of time. The resultant power use is thus greater than that of a sleeping mechanical mouse. There is thus a need for alternative methods and systems that sense when a mouse (or other input device) is needed and wake the device. Proximity detection is one such alternative. Instead of sampling the mouse's (or device's) motion detector elements for movement, detection of a user's approaching hand can be used as an indicator that the mouse must wake up.
Various types of user proximity detectors are known and used in power management systems and other applications. For example, Mese et al. U.S. Pat. No. 5,396,443 discloses power saving control arrangements for an information processing apparatus. More specifically, the Mese et al. patent describes various systems for (1) detecting the approach (or contact) of a user associated medium to (or with) the apparatus; (2) placing a controlled object of the apparatus in a non-power saving state when such contact or approach is detected; and (3) placing the controlled object in a power saving state when the presence of the user associated medium (i.e., a stylus pen or part of a user's body) is not detected for a predetermined period of time. The '443 patent describes various types of approach/contact sensors. Among these, various “tablet” type sensor systems are described, including electromagnetic, capacitance, and electrostatic coupling tablets. In one embodiment, a contact or approach detecting tablet, and a flat display panel, may be integrally formed with a housing of the information processing apparatus.
Sellers U.S. Pat. No. 5,669,004 discloses a system for reducing power usage in a personal computer. More specifically, a power control circuit is disclosed for powering down portions of a personal computer in response to user inactivity, and for delivering full power to these portions once user activity is detected via one or more sensors. The components to which power is reduced (or removed) are components which can respond almost immediately to being turned on. On the other hand, components which require a period of time to come up to full operation (e.g., disk drive motors, monitor, main processor) are driven to full power. In the primary embodiment that is disclosed, the sensor is a piezoelectric sensor fitted into a keyboard. Sellers discloses that sensors may be positioned at other locations on the computer (a monitor, mouse, trackball, touch pad or touch screen) and that various other kinds of sensors (capacity, stress, temperature, light) could be used instead of piezoelectric sensors.
Commonly owned U.S. patent application Ser. No. 09/948,099, filed Sep. 7, 2001, discloses capacitive sensing and data input device power management systems and methods. In the disclosed embodiments, capacitive proximity sensing is carried out by detecting a relative change in the capacitance of a “scoop” capacitor formed by a conductor and surrounding ground plane. The conductor may be a plate provided in the form of an adhesive label printed with conductive ink. Charge is transferred between the scoop capacitor and a relatively large “bucket” capacitor, and a voltage of the bucket capacitor is applied to an input threshold switch. A state transition from low to high (or high to low) of the input threshold is detected, and a value indicative of the number of cycles of charge transfer required to reach the state transition is determined. The presence or absence of an object or body portion in close proximity to or in contact with a device can be determined by comparing the value with a predetermined threshold. The predetermined threshold can be adjusted to take into account environmentally induced changes in capacitance of the scoop capacitor.